The broad objective of this project is to use conventional and molecular techniques to define the virologic events following smallpox vaccination in vaccinia-naive and vaccinia-experienced individuals. The specific alms are to: 1) Define the virologic events associated with smallpox vaccination. 2) Determine whether multiple viral variants are present within the Dryvax vaccine, and if so, to investigate their role in the virology of smallpox vaccination and in adverse reactions. 3) Define the virologic events associated with adverse reactions to smallpox vaccination. 4) Examine the virologic response to treatment with vaccinia immune globulin (VIG) and/or cidofovir in vaccinees who require these therapies to control adverse reactions. A quantitative real-time PCR assay will be developed and used to measure the level of vaccinia DNA at regular intervals after vaccination. Specimens will also be cultured for vaccinia virus. These studies will be useful for defining the possible contagiousness of individuals having smallpox vacciniation and for helping determine the need for donor deferral for voluntary blood donations. The data will also provide a basis for studies of the immunology and immunogentics of vaccinia. Studies will be performed of Dryvax vaccine to define variants within the vaccine virus. In collaboration with the Genome Sequencing Center, the complete nucleotide sequence of 5 variant strains will be determined. Specific assays will be developed and used to define the contribution of variants to immunogenicity and reactogenicity of the vaccine. Smallpox adverse reaction clinics will be established at each participating medical center to evaluate individuals with possible adverse reactions. Individuals seen in these clinics will be recruited to participate in detailed studies of the virology, immunology, and immunogenetics of smallpox vaccination. These studies will investigate the virology of adverse reactions, the relationship between viral and immunologic events, and the genetic basis for both. For individuals having severe adverse reactions, virologic studies will be used to help evaluate and guide therapy with VIG and cidofovir. The studies described will form a basis for evaluating Dryvax as well as future smallpox vaccines. The assays to be developed and the clinics to be established will provide an infrastructure that will be available to respond to a bioterrorist attack on the United States.